Image forming apparatus controlling density of an output image

ABSTRACT

An image forming apparatus includes a conversion unit configured to convert image data based on a conversion condition, an image forming unit configured to form an image on a sheet based on the converted image data, a detection unit configured to detect a pattern image on a transfer member, a reading unit configured to read a test image formed on a sheet, a controller configured to perform calibration based on a reading result of the reading unit, and a reception unit. In a case where the calibration is performed, the controller determines an image forming condition based on a result of detection by the detection unit before the test image is formed. In a case where the reception unit receives the discontinuation instruction, the controller changes the image forming condition to an image forming condition before the pattern image is formed.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.17/153,653 filed Jan. 20, 2021, which claims priority from JapanesePatent Application No. 2020-129569, filed Jul. 30, 2020, which is herebyincorporated by reference herein in its entirety.

BACKGROUND OF THE DISCLOSURE Field of the Disclosure

The aspect of the embodiments relates to density control to controldensity of an image formed by an image forming apparatus.

Description of the Related Art

It is known that density of an image formed by an image formingapparatus is varied due to an environmental condition (temperature andhumidity), and wear of parts. A common image forming apparatus thus canform a test image and perform a calibration function of controllingdensity of an output image based on a result of reading the test imageby a reading device.

As a method of controlling the density of an image formed by an imageforming apparatus, a method of controlling an image forming conditionand a method of controlling an image processing condition (conversioncondition) are known.

As the image forming condition, for example, a charging voltage to beapplied to a charging member charging a photosensitive body, laser powerof a light source exposing the photosensitive body, and a developmentvoltage to be applied to a developing sleeve developing an electrostaticlatent image are known. An image forming apparatus can change themaximum density of an output image by change of the image formingcondition. It is known that, on the other hand, controlling the imageforming condition causes the low to halftone density of the output imageto deviate from the ideal density.

The image processing condition (conversion condition) is, for example, aone-dimensional table or a function that represents relationship betweenan input value and an output value used to convert image datatransferred to the image forming apparatus. The image forming apparatuscan change the wide range from the low density to high density of theoutput image if the image processing condition (conversion condition) ischanged. Even if the image processing condition (conversion condition)is controlled, however, there is an upper limit to a range where themaximum density is changeable.

Accordingly, a common image forming apparatus controls the density ofthe output image by changing both of the image forming condition and theimage processing condition (conversion condition). An image formingapparatus discussed in U.S. Pat. No. 6,418,281 controls the imageforming condition based on a reading result of a first test image, andthen controls the image processing condition (conversion condition)based on a reading result of a second test image. The image formingapparatus forms the second test image based on the image formingcondition determined based on the reading result of the first testimage.

In an image forming apparatus, calibration may be cancelled in themiddle of being executed. For example, a possible reason is that a sheeton which a test image has been formed may be jammed inside the imageforming apparatus, and a user turns off the main power supply of theimage forming apparatus. Another possible reason is that even though thecalibration has been executed halfway through, a user instructs theimage forming apparatus via an operation panel to cancel the calibrationin the middle of being executed in a case where the user desires toexecute printing in the image forming apparatus immediately.

In a case where the calibration is canceled in the middle of beingexecuted, although the image forming condition has been updated, theimage processing condition (conversion condition) may not be updated. Inthis case, since only the image forming condition is updated, the low tohalftone density of the output image is deviated from the ideal density.

SUMMARY OF THE DISCLOSURE

According to an aspect of the embodiments, an image forming apparatusincludes a conversion unit configured to convert image data based on aconversion condition, an image forming unit configured to form an imageon a sheet based on the converted image data, a transfer member ontowhich a pattern image formed by the image forming unit is transferred, adetection unit configured to detect the pattern image formed on theintermediate transfer member, a reading unit configured to read a testimage formed on a sheet, a controller configured to perform calibration,in which the conversion condition is generated based on a result ofreading the test image by the reading unit, and a reception unitconfigured to receive an instruction to discontinue the calibration. Ina case where the calibration is performed, the controller determines animage forming condition for controlling density of an image to be formedby the image forming unit based on a result of detection by thedetection unit before the test image is formed. In a case where thereception unit receives the discontinuation instruction during a periodfrom when the image forming condition is determined based on thedetection result of the detection unit until the conversion condition isgenerated based on the result of reading the test image, the controllerchanges the image forming condition to an image forming condition beforethe pattern image is formed.

Further features of the disclosure will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of an image formingapparatus.

FIG. 2 is a control block diagram of the image forming apparatus.

FIG. 3 is a flowchart illustrating calibration.

FIGS. 4A, 4B, and 4C are diagrams each illustrating an example of a userinterface (UI) for the calibration.

FIG. 5 is a schematic view illustrating test charts.

FIG. 6 is a flowchart illustrating a first sequence of the calibration.

FIG. 7 is a flowchart illustrating a second sequence of the calibration.

FIG. 8 is a diagram illustrating an example of a UI to instructdiscontinuation of the calibration.

FIG. 9 is a flowchart illustrating calibration according to anotherexemplary embodiment.

FIGS. 10A, 10B, and 10C are tables each illustrating a combination of animage forming condition and a gradation correction condition.

FIG. 11 is an exemplary diagram illustrating a UI for calibrationperformed in automatic document feeder (ADF) reading.

FIGS. 12A to 12D are exemplary diagrams each illustrating a UI forcalibration performed in platen reading.

DESCRIPTION OF THE EMBODIMENTS

Elements of one embodiment may be implemented by hardware, firmware,software or any combination thereof. The term hardware generally refersto an element having a physical structure such as electronic,electromagnetic, optical, electro-optical, mechanical,electro-mechanical parts, etc. A hardware implementation may includeanalog or digital circuits, devices, processors, applications specificintegrated circuits (ASICs), programmable logic devices (PLDs), fieldprogrammable gate arrays (FPGAs), or any electronic devices. The termsoftware generally refers to a logical structure, a method, a procedure,a program, a routine, a process, an algorithm, a formula, a function, anexpression, etc. The term firmware generally refers to a logicalstructure, a method, a procedure, a program, a routine, a process, analgorithm, a formula, a function, an expression, etc., that isimplemented or embodied in a hardware structure (e.g., flash memory,ROM, EROM). Examples of firmware may include microcode, writable controlstore, micro-programmed structure.

When implemented in software or firmware, the elements of an embodimentmay be the code segments to perform the necessary tasks. Thesoftware/firmware may include the actual code to carry out theoperations described in one embodiment, or code that emulates orsimulates the operations. The program or code segments may be stored ina processor or machine accessible medium. The “processor readable oraccessible medium” or “machine readable or accessible medium” mayinclude any non-transitory medium that may store information. Examplesof the processor readable or machine accessible medium that may storeinclude a storage medium, an electronic circuit, a semiconductor memorydevice, a read only memory (ROM), a flash memory, an erasableprogrammable ROM (EPROM), a floppy diskette, a compact disk (CD) ROM, anoptical disk, a hard disk, etc. The machine accessible medium may beembodied in an article of manufacture. The machine accessible medium mayinclude information or data that, when accessed by a machine, cause themachine to perform the operations or actions described above. Themachine accessible medium may also include program code, instruction orinstructions embedded therein. The program code may include machinereadable code, instruction or instructions to perform the operations oractions described above. The term “information” or “data” here refers toany type of information that is encoded for machine-readable purposes.Therefore, it may include program, code, data, file, etc.

All or part of an embodiment may be implemented by various meansdepending on applications according to particular features, functions.These means may include hardware, software, or firmware, or anycombination thereof. A hardware, software, or firmware element may haveseveral modules coupled to one another. A hardware module is coupled toanother module by mechanical, electrical, optical, electromagnetic orany physical connections. A software module is coupled to another moduleby a function, procedure, method, subprogram, or subroutine call, ajump, a link, a parameter, variable, and argument passing, a functionreturn, etc. A software module is coupled to another module to receivevariables, parameters, arguments, pointers, etc. and/or to generate orpass results, updated variables, pointers, etc. A firmware module iscoupled to another module by any combination of hardware and softwarecoupling methods above. A hardware, software, or firmware module may becoupled to any one of another hardware, software, or firmware module. Amodule may also be a software driver or interface to interact with theoperating system running on the platform. A module may also be ahardware driver to configure, set up, initialize, send and receive datato and from a hardware device. An apparatus may include any combinationof hardware, software, and firmware modules.

FIG. 1 is a cross-sectional view of an image forming apparatus 1000. Theimage forming apparatus 1000 includes a reader A and a printer B. Thereader A includes an automatic document feeder (hereinafter, referred toas ADF) 100, an image reading unit 200, and a reader controller 211. Thereader A can perform ADF reading to read a document conveyed by the ADF100, and platen reading to read a document placed on a platen 202.

First, a configuration and operation of the ADF 100 will be described.When a document reading job by the ADF 100 is started, a carriage 209moves to a position just below a white reference plate 219, and shadingoperation is performed. After the shading operation is performed, thecarriage 209 moves to a position just below an ADF reading portion 201of the platen 202, and stands by at the position. When the documentreading job is started, a feeding roller 1 first falls on a documentsurface of a document bundle S including a plurality of sheets(documents), and starts to rotate. As a result, a document on the top ofthe document bundle is fed.

The ADF 100 includes a tray 30 that is a placement portion on which thedocument bundle S is placed. The ADF 100 feeds the documents one by onefrom the one on the top of the document bundle S placed on the tray 30.At this time, feeding of the documents is performed while a separationroller 2, a separation pad 8, and the feeding roller 1 prevent adocument other than the one on the top from being overlapped thereon andbeing conveyed. In other words, the documents fed by the feeding roller1 are separated one by one by action of the separation roller 2 and theseparation pad 8. The feeding roller 1 conveys the separated document toa roller 3. After the document abuts on the roller 3, a loop is formedat the leading edge of the document, which eliminates skewing of adocument.

A roller 4 is provided on a downstream side of the roller 3. A path toconvey the document is provided from the roller 4 to the ADF readingportion 201. The document sent to the path is sent to the roller 4 bythe roller 3. After passing the roller 4, the document is conveyed so asto pass through the ADF reading portion 201 near a platen roller 5.

When the document is conveyed to the ADF reading portion 201, a leadingedge of the document is detected by a read sensor 14. The ADF 100 countsa time from a timing when the read sensor 14 is ON until a timing whenthe document reaches the ADF reading portion 201 by using a clock of amotor (not illustrated) that serves as a driving source of the roller 4and the platen roller 5. As described above, in the case where the ADFreading is performed, the reader A starts to read the document at thetiming when the leading edge of the document reaches the ADF readingportion 201.

When a trailing edge of the document is detected by a post-separationsensor 12, the ADF 100 detects presence or absence of a document on thetray 30 by a document detection sensor 16. When the document is furtherconveyed after the trailing edge of the document passes through theplaten roller 5 and a roller 6, the trailing edge of the document isdetected by a sheet discharge sensor 15. The document is discharged ontoa document discharge tray 31 by a sheet discharge roller 7 at a timingwhen the trailing edge of the document is detected by the sheetdischarge sensor 15. The document reading job (ADF reading) for readingone side of one sheet of document is ended.

As described above, in the case of the ADF reading, the ADF 100 conveysthe documents placed on the tray 30 to the ADF reading portion 201 oneby one. The image reading unit 200 moves the carriage 209 to theposition just below the ADF reading portion 201, and reads the documentat the position when the document is being conveyed. In contrast, in thecase of the platen reading, the image reading unit 200 reads thedocument by the carriage 209 scanning the document placed on the platen200 in an arrow a direction illustrated in FIG. 1 .

As described above, the document placed on the ADF 100 or the documentplaced on the platen 202 is read by an optical system through the platen202. The optical system includes reflecting mirrors 205 and 206, a lens207, and a charge-coupled device (CCD) sensor 210 in addition to thecarriage 209 including a light source lamp 203 and a reflecting mirror204. Image information read by the CCD sensor 210 is photoelectricallyconverted into an electric signal data array, and the electric signaldata array is further converted into an image signal by the readercontroller 211. In the present exemplary embodiment, a carriage movingtype reader in which the CCD sensor 210 does not move but the carriage209 moves to read the document is described as the image reading unit200. The present exemplary embodiment, however, is not limited to theconfiguration. The image reading unit 200 may be, for example, a sensormoving type reader in which a contact image sensor (CIS) reads thedocument while moving.

The white reference plate 219 is a white plate for creating referencedata of a white level in shading correction processing. Immediatelyafter the document reading job is started, the image reading unit 200moves the carriage 209 to the position just below the white referenceplate 219, and reads the white reference plate 219 to perform theshading correction processing. An image signal on which the shadingcorrection processing has been performed is output to a printercontroller 109 of the printer B. At this time, the image signal includesrespective pieces of luminance information on red (R), green (G), andblue (B).

The reader A can read a test chart placed on the platen 202 in place ofthe document. Further, the reader A can read the test chart placed onthe tray 30 in place of the document while the test chart is beingconveyed by the ADF 100.

In addition, a jam, i.e., conveyance failure of the document, may occurin the ADF 100. For example, the reader controller 211 determineswhether conveyance failure of the document has occurred from eachdetection result and detection timing of the post-separation sensor 12,the read sensor 14, the sheet discharge sensor 15, and conveyancesensors 17 and 13. For example, in a case where the passing timing ofthe leading edge/trailing edge of the document is later than normaltiming, or in a case where the leading edge/trailing edge of thedocument is not detected, it is determined that conveyance failure ofthe document has occurred.

Next, a configuration and operation of the printer B will be described.The printer B includes an image forming unit 120 forming a yellow image,an image forming unit 130 forming a magenta image, an image forming unit140 forming a cyan image, and an image forming unit 150 forming a blackimage. Since each of the image forming units 120, 130, 140, and 150 hasa similar configuration, the configuration of the yellow image formingunit 120 will be described here. The yellow image forming unit 120includes a photosensitive drum 121, a charger 122, a developing device123, and a transfer blade 124.

The photosensitive drum 121 is a drum including a photosensitive layerformed on a surface thereof. The photosensitive drum 121 is rotationallydriven in a predetermined direction by a motor (not illustrated). Thecharger 122 is a corona charger including a wire and a grid electrode.The charger 122 may be a roller charger. A charging voltage is appliedto the charger 122, and the charger 122 uniformly charges thephotosensitive drum 121. When the charged photosensitive drum 121 isscanned with light radiated from a laser scanner, an electrostaticlatent image is formed on the photosensitive drum 121. The developingdevice 123 includes a developing sleeve and an agitation member, anddevelops the electrostatic latent image formed on the photosensitivedrum 121 by using toner.

The image signal input from the reader A is converted by the printercontroller 109 into a pulse width modulation (PWM) signal. The PWMsignal is a driving signal driving a laser beam radiated from the laserscanner 110. Further, in a case where image data is transferred from anexternal device, the printer controller 109 also converts an imagesignal of the image data into a PWM signal and drives a semiconductorlaser 410 (FIG. 2 ) of the laser scanner 110.

A sheet stored in a cassette 126 is fed to a conveyance path and thenconveyed to a transfer belt 111. The transfer belt 111 electrostaticallyattracts and conveys the sheet. The transfer blade 124 discharges from arear surface of the transfer belt 111 and transfers a toner image on thephotosensitive drum 121 onto the sheet being conveyed on the transferbelt 111. The sheet on which the toner images have been transferred fromthe photosensitive drums 121, 131, 141, and 151 is conveyed to a fixingdevice 114. The fixing device 114 melts the toner images on the sheet byheat from a heater to fix the toner images onto the sheet. The sheet towhich the toner images have been fixed is discharged from the printer B.

The photosensitive drums 121, 131, 141, and 151 respectively includesurface electrometers 125, 135, 145, and 155 each measuring a surfacepotential on the surface of the corresponding photosensitive drum. Thesurface electrometers 125, 135, 145, and 155 are used to adjust acontrast potential.

The image forming apparatus 1000 measures a pattern image that is formedon the transfer belt 111 by using a sensor 160 without being transferredonto the sheet. The sensor 160 is, for example, an optical sensordetecting reflected light from the pattern image formed on the transferbelt 111. The sensor 160 outputs an output value according to intensityof the reflected light. The output value of the sensor 160 is convertedinto density information based on a density conversion table previouslystored. The density information is input to the printer controller 109.At this time, the transfer belt 111 functions as an intermediatetransfer member to which the pattern image is transferred.

(Printer Controller)

FIG. 2 is a control block diagram of the image forming apparatus 1000. Acentral processing unit (CPU) 401 functions as a controller totallycontrolling units of the image forming apparatus 1000. A memory 402includes a read only memory (ROM) and a random access memory (RAM), andstores a control program and various kinds of data. An operation panel Uis a touch panel display in which a display and input keys areintegrated.

The image signal output from the reader A is input to a color processingunit 403 of the printer controller 109. The color processing unit 403performs color processing on the input image signal to obtain a desiredoutput image in a case where the output characteristics of the printer Bare ideal. The color processing unit 403 converts the input signal(luminance signal) of red (R), green (G), and blue (B) into an imagesignal (density signal) of yellow (Y), magenta (M), and cyan (C) byusing an LUTid 404. The LUTid 404 is a conversion table to convert theluminance signal into the density signal. The image signal (densitysignal) of yellow (Y), magenta (M), and cyan (C) is output to an imageprocessing unit 411.

The image processing unit 411 includes an under color removal (UCR) unit405 and a gamma correction circuit 406. The UCR unit 405 performs undercolor removal processing for generating an image signal (density signal)of black (Bk) from the image signal (density signal) of yellow (Y),magenta (M), and cyan (C). The gamma correction circuit 406 converts theimage signal to correct a density characteristic (gradationcharacteristic) of the printer B to an ideal density characteristic(ideal gradation characteristic). The image processing unit 411 convertsthe image signal by using a gradation correction condition (LUTa)corresponding to a type of a screen used in dither processing (halftoneprocessing). The LUTa is a one-dimensional conversion table representingcorrespondence relationship between an input value and an output valueof the image signal. As described above, the gradation characteristic ofthe image formed on the sheet by the printer B is varied depending onenvironmental change and wear of parts. Further, the gradationcharacteristic of the image is varied depending on a type of the screen.The CPU 401 thus performs calibration to update the LUTa, and maintainsthe gradation characteristic of the image at predetermined gradationcharacteristic. The printer B is an example of an image forming unitthat forms a toner image on a sheet based on an image signal correctedby the gamma correction circuit 406. The memory 402 may hold a LUTa foreach type of sheet. The CPU 401 reads out the LUTa corresponding to thetype of the sheet designated via the operation panel U from the memory402, and sets the LUTa to the gamma correction circuit 406. The LUTa isused when a document is copied and when an image is formed based on aprint job from a host computer, but is not used when the calibration isperformed.

The image signal output from the image processing unit 411 is input to adither processing unit 407. The dither processing unit 407 performs thedither processing (halftone processing) on the output image signalsdetermined based on the LUTa inside the gamma correction circuit 406,and outputs a resultant image signal to a PWM unit 408. The ditherprocessing unit 407 performs the dither processing to convert the 10-bitimage signal into 4-bit data. The PWM unit 408 generates a drivingsignal pulse-width modulated based on the image signal, and outputs thedriving signal to a laser driver 409. The laser driver 409 causes thesemiconductor laser 410 to emit light based on the driving signal.

A high voltage circuit 412 charges the surface of the photosensitivedrum 121 to a predetermined potential, and controls high voltageapplication in the developing device 123 and the transfer blade 124.

(Calculation of Image Forming Condition)

The CPU 401 determines an image forming condition before updating theLUTa. In the following, for example, a surface potential (VD) of acharged area on the photosensitive drum 121 and intensity of the laserbeam (LPW) emitted from the semiconductor laser 410 of the laser scanner110 are determined as the image forming condition.

The CPU 401 forms pattern images with different densities on thetransfer belt 111. The pattern images with the different densities areformed by change of the charging voltage and the laser power LPW. TheCPU 401 causes the sensor 160 to measure reflected light from thepattern images with different densities, and calculates the surfacepotential VD and the laser power LPW from the densities of the patternimages and target densities. The CPU 401 controls the image formingapparatus 1000 based on the calculated image forming conditions.

(Calibration)

In the following, the calibration to generate the gradation correctioncondition by using the test chart will be described. The CPU 401 causesthe image forming apparatus 1000 to form a test image on a sheet bysupplying a predetermined image signal (density signal) to the ditherprocessing unit 407. The sheet on which the test image has been formedis referred to as a test chart. The reader A reads the test chart, andthe reader controller 211 transfers read data to the printer controller109.

The printer controller 109 converts the read data of the test chart intodensity signal values. At this time, the printer controller 109generates a density signal value of a yellow test image from a luminancesignal value of blue (B) in the read data of the yellow test image. Theprinter controller 109 generates a density signal value of a magentatest image from a luminance signal value of green (G) in the read dataof the magenta test image. The printer controller 109 generates adensity signal value of a cyan test image from a luminance signal valueof red (R) in the read data of the cyan test image. The printercontroller 109 generates a density signal value of a black test imagefrom a luminance signal value of green (G) in the read data of the blacktest image.

Next, the CPU 401 generates the LUTa such that the correspondencerelationship (gradation characteristic) between the input value of theimage signal used for formation of the test image and the density signalvalues acquired via the reader A becomes an ideal gradationcharacteristic. The LUTa is generated for each of the colors of yellow(Y), magenta (M), cyan (C), and black (Bk).

As described above, the reader A can perform both of the platen readingand the ADF reading. The reader A thus may perform the platen reading orthe ADF reading on the test chart. In one embodiment, the ADF readingmay be performed because the workload of an operator (user) is less inthe ADF reading than in the platen reading.

FIG. 3 is a flowchart illustrating calibration processing.

The calibration processing is performed, for example, when the CPU 401reads out a program stored in the memory 402 in response to acalibration execution instruction from the operation panel U. In stepS501, the CPU 401 displays a reading method selection screen on theoperation panel U. When a user selects a reading method on the selectionscreen of the operation panel U, the CPU 401 acquires information aboutwhether the reading method selected by the user is the ADF reading orthe platen reading.

FIG. 4A illustrates the selection screen (UI 700 a) displayed on theoperation panel U. In step S501, the CPU 401 displays the selectionscreen (UI 700 a) on the display of the operation panel. The UI 700 a isthe selection screen, which includes a button 701 a for selecting theADF reading and a button 701 b for selecting the platen reading.

In step S502, the CPU 401 determines whether the user has selected theADF reading based on the acquired information. In a case where the ADFreading has been selected in step S502 (YES in step S502), theprocessing proceeds to step S503, and the CPU 401 performs a firstsequence. In contrast, in a case where the platen reading has beenselected in step S502 (NO in step S502), the processing proceeds to stepS507, and the CPU 401 performs a second sequence.

(First Sequence)

In step S503, the CPU 401 calculates the image forming condition fromthe detection result of the pattern image by the sensor 160. Here, VDnand LPWn are calculated as the image forming conditions. In step S504,the CPU 401 causes the printer B to form the test image on a sheet basedon the test image data. In step S504, the image signal of the test imagedata is supplied to the dither processing unit 407, and the printer Bdischarges the sheet (test chart) on which the test image has beenformed.

FIG. 5 illustrates examples of the test chart. Test charts 801 a and 801b each include a test image including ten gradations for each of thecolors Y, M, C, and Bk. For example, the ten gradations are respectivelyformed by image signals of 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%,and 100%. The dither processing unit 407 may perform a plurality ofhalftone processing. For example, the dither processing unit 407 mayinclude a screen with low screen rulings (160 lpi to 180 lpi) and ascreen with high screen rulings (250 lpi to 300 lpi). Here, “lpi” is anabbreviation for lines/inch. In a case where the LUTa for the pluralityof halftone processes is generated, for example, an LUTa1 correspondingto the screen with low screen rulings and an LUTa2 corresponding to thescreen with high screen rulings are generated.

The test chart 801 a is a test chart to which the screen with low screenrulings has been applied. The test chart 801 b is a test chart to whichthe screen with high screen rulings has been applied. The screen withlow screen rulings is applied to a photographic image, etc., while thescreen with high screen rulings is applied to characters, etc. Theprinter B may form an image with three or more types of screen rulings.

For example, the CPU 401 displays a UI 700 d illustrated in FIG. 11 onthe operation panel U. The UI 700 d includes a message that prompts theuser to check presence of two or more sheets in the cassette 126, amessage indicating that two test charts are successively printed, and abutton 701 d for instructing start of printing. When start of printingis instructed, the CPU 401 sets the screen with low screen rulings tothe dither processing unit 407, and outputs an image signal (test imagesignal) of the test image to the dither processing unit 407. The ditherprocessing unit 407 performs the halftone processing on the test imagesignal based on the screen with low screen rulings. As a result, the10-bit test image signal is converted into a 4-bit test image signal.The printer B prints the test chart 801 a based on the test image signaloutput from the dither processing unit 407. Next, the CPU 401 sets thescreen with high screen rulings to the dither processing unit 407, andoutputs a test image signal to the dither processing unit 407. Thedither processing unit 407 performs the halftone processing on the testimage signal based on the screen with high screen rulings. As a result,the 10-bit test image signal is converted into a 4-bit test imagesignal. The printer B prints the test chart 801 b based on the testimage signal output from the dither processing unit 407.

When start of reading is instructed from the operation panel U after theuser places the test charts 801 a and 801 b on the tray 30, in stepS505, the CPU 401 operates the ADF 100 to perform the ADF reading. Forexample, when the test charts 801 a and 801 b are output in step S504,the CPU 401 displays a message that prompts the user to place the testcharts on the tray 30 on the operation panel U. As illustrated in FIG.4B, a UI 700 b that includes the message and a button 701 c forinstructing start of reading is displayed on the operation panel U.

After the reader A reads the test charts 801 a and 801 b in the ADFreading in step S505, the reader controller 211 of the image readingunit 200 outputs read data to the printer controller 109. Thereafter,the processing proceeds to step S506.

In step S506, the CPU 401 generates the LUTa1 and the LUTa2 such thatthe gradation characteristics of the output images corresponding to therespective screens determined from the read data of the test charts 801a and 801 b become the ideal gradation characteristics. Thereafter, theCPU 401 updates the image forming conditions with VDn and LPWn, alsoupdates the LUTa1 and the LUTa2, and then ends the calibrationprocessing.

(Second Sequence)

In step S507, the CPU 401 calculates the image forming condition fromthe detection result of the pattern image by the sensor 160. Here, thecalculated image forming conditions are VDn and LPWn. In step S508, theCPU 401 causes the printer B to form the test image on a sheet based onthe test image data. In step S508, the image signal of the test imagedata is supplied to the dither processing unit 407, and the test chart801 a is discharged.

For example, the CPU 401 displays a UI 700 f illustrated in FIG. 12A onthe operation panel U. The UI 700 f includes a message that prompts theuser to check presence of two or more sheets in the cassette 126, amessage indicating that the first test chart 801 a is printed, and thebutton 701 d. When start of printing is instructed, the CPU 401 sets thescreen with low screen rulings to the dither processing unit 407, andoutputs an image signal of the test image (test image signal) to thedither processing unit 407. The dither processing unit 407 performs thehalftone processing on the test image signal based on the screen withlow screen rulings. As a result, the 10-bit test image signal isconverted into a 4-bit test image signal. The printer B prints the testchart 801 a based on the test image signal output from the ditherprocessing unit 407.

In a case where start of reading is instructed from the operation panelU after the user places the test chart 801 a on the platen 202, then instep S509, the CPU 401 performs the platen reading. For example, whenthe test chart is output in step S508, the CPU 401 displays a messagethat prompts the user to place the test chart on the platen 202 on theoperation panel U. As illustrated in FIG. 4C, a UI 700 c that includesthe message and the button 701 c for instructing start of reading isdisplayed on the operation panel U. The operator opens the ADF 100 sothat the platen 202 is exposed, places the test chart on the platen 202,and then presses the reading start button 701 c of the operation panelU. When the instruction to start of reading is input from the operationpanel U, the CPU 401 causes the reader A to perform the platen reading.As a result, the reader controller 211 of the image reading unit 200outputs read data to the printer controller 109. Thereafter, theprocessing proceeds to step S510.

For example, the CPU 401 displays a UI 700 g illustrated in FIG. 12B onthe operation panel U. The UI 700 g includes a message that prompts theuser to place the first test chart 801 a on the platen 202, and thebutton 701 c. The CPU 401 causes the image reading unit 200 to read thetest chart 801 a in response to pressing of the button 701 c of the UI700 g. The reader controller 211 outputs a luminance signal representingthe reading result to the printer controller 109.

In step S510, the CPU 401 generates the LUTa1 such that the gradationcharacteristic of the output image corresponding to the screen with lowscreen rulings determined from the read data of the test chart 801 abecomes the ideal gradation characteristic. Next, in step S511, the CPU401 determines whether reading of all of the test charts has beencompleted. In a case where the test chart 801 b for the screen with highscreen rulings has not been read (NO in step S511), the processingreturns to step S508, and the CPU 401 causes the printer B to output thetest chart 801 b.

For example, the CPU 401 displays a UI 700 h illustrated in FIG. 12C onthe operation panel U. The UI 700 h includes a message indicating thatthe second test chart 801 b is printed, and the button 701 d. When startof printing is instructed, the CPU 401 sets the screen with high screenrulings to the dither processing unit 407, and outputs the test imagesignal to the dither processing unit 407. The dither processing unit 407performs the halftone processing on the test image signal based on thescreen with high screen rulings. As a result, the 10-bit test imagesignal is converted into a 4-bit test image signal. The printer B printsthe test chart 801 b based on the test image signal output from thedither processing unit 407.

For example, the CPU 401 displays a UI 700 i illustrated in FIG. 12D onthe operation panel U. The UI 700 i includes a message that prompts theuser to place the second test chart 801 b on the platen 202, and thebutton 701 c. The CPU 401 causes the image reading unit 200 to read thetest chart 801 b in response to pressing of the button 701 c of the UI700 i. The reader controller 211 of the image reading unit 200 outputs aluminance signal indicating the reading result to the printer controller109.

In contrast, in a case where reading of all of the test charts 801 a and801 b has been completed in step S511 (YES in step S511), the CPU 401updates the image forming conditions with VDn and LPWn, also updates theLUTa1 and the LUTa2, and then ends the calibration processing.

(Discontinuation of Calibration)

Discontinuation of the calibration will be described below. In the casewhere test charts are read in the ADF reading, a plurality of testcharts is read at a time as described in FIG. 3 . The plurality of testcharts is thus output at a time. Before the output test charts are readin the ADF reading, the CPU 401 displays a UI illustrated in FIG. 8 onthe operation panel U to check whether the user desires to discontinueformation of the test images. In a case where discontinuation of thecalibration is instructed in the UI illustrated in FIG. 8 during thefirst sequence, an instruction to discontinue formation of the testimages is input to the CPU 401. When the CPU 401 receives thediscontinuation instruction, the CPU 401 discontinues the calibration.In the case where the calibration is discontinued, the CPU 401 returnsthe image forming condition to an original image forming conditionbefore the pattern image is formed.

In a case where a jam occurs in the ADF 100 or in a case where the ADF100 is turned off before reading of the test charts, the instruction todiscontinue formation of the test images is also input to the CPU 401.

In contrast, in the case where the test charts are read in the platenreading, one test chart is output, and a test chart of other screen isnot output until the output test chart is read. Therefore, the CPU 401displays the UI illustrated in FIG. 8 on the operation panel U beforeeach of the test charts is read to check whether the user desires todiscontinue formation of the test images. In a case wherediscontinuation of the calibration is instructed via the UI illustratedin FIG. 8 during the second sequence, an instruction to discontinueformation of the test images is input to the CPU 401. Accordingly, theCPU 401 discontinues the calibration, and returns the image formingcondition to an original image forming condition before the patternimage is formed.

In the case where the calibration is discontinued, a state where theimage forming condition is changed but the gradation coefficientcondition is not updated unless the image forming conditions (LPW andVD) are not returned to the image forming conditions before thediscontinuation. As a result, the density of the output image cannot becontrolled to the target density.

(Processing in Case of Discontinuation of Calibration)

In a case where the discontinuation instruction is received during aperiod from when the image forming conditions are determined based onthe detection result of the sensor 160 until the gradation correctioncondition (LUTa) is generated, the CPU 401 changes the image formingconditions to the image forming conditions before the pattern image isformed. In the following, a case where the calibration is discontinuedin the middle of the first sequence will be described with reference toa flowchart illustrating the first sequence in FIG. 6 .

In step S901, the CPU 401 causes the printer B to form the patternimage, causes the sensor 160 to detect the pattern image on the transferbelt 111, and calculates the image forming conditions based on thedetection result of the sensor 160. In step S902, the CPU 401 changesthe image forming conditions to VDn and LPWn. The CPU 401 stores theimage forming conditions (VDn and LPWn) calculated in step S901 and theimage forming conditions (VDo and LPWo) used before the pattern image isformed in respectively different areas of the memory 402.

Next, in step S903, the CPU 401 causes the printer B to output the twotest charts 801 a and 801 b (FIG. 5 ). Before the test charts 801 a and801 b (FIG. 5 ) are printed, the CPU 401 displays the UI (FIG. 8 ) forthe user to instruct discontinuation of the calibration on the displayof the operation panel U. In step S904, the CPU 401 determines whetherdiscontinuation of the calibration has been instructed before the testcharts 801 a and 801 b are read. In response to selection of thediscontinuation of the calibration by the user on the UI of FIG. 8 , theoperation panel U transmits the discontinuation instruction to the CPU401.

In a case where the CPU 401 does not receive the discontinuationinstruction and start of reading is instructed in step S904 (NO in stepS904), the CPU 401 reads the test charts 801 a and 801 b in the ADFreading in step S905. In step S906, the CPU 401 generates the gradationcorrection conditions (LUTa1 and LUTa2), updates the gradationcorrection conditions (LUTa1 and LUTa2) stored in the memory 402, andends the calibration processing.

In contrast, in a case where the CPU 401 receives the discontinuationinstruction in step S904 (YES in step S904), then in step S907, the CPU401 reads out the image forming conditions used before the pattern imageis formed, from the memory 402, and resets the image forming conditionsto the original values (VDo and LPWo). Thereafter, the CPU 401 ends thecalibration processing.

How the discontinuation is instructed is not limited to theconfiguration in which the discontinuation instruction is transmitted inresponse to operation of the operation panel U by the user. For example,in a case where a jam occurs in the printer B while the printer Boutputs the test chart 801 a (or test chart 801 b), the CPU 401 receivesthe discontinuation instruction. Further, for example, in a case where ajam occurs in the ADF 100 while the ADF 100 conveys the test chart 801 a(or test chart 801 b), the discontinuation instruction is alsotransmitted from the reader controller to the CPU 401. Further, forexample, in a case where a main power supply of the image formingapparatus 1000 is turned off during a period from when the image formingconditions are determined based on the detection result of the sensor160 until the gradation correction condition (LUTa) is generated basedon the reading result of the test image, the CPU 401 receives thediscontinuation instruction. In a case where the CPU 401 receives thediscontinuation instruction during the first sequence, the CPU 401resets the image forming conditions to the original values (VDo andLPWo), and ends the calibration processing.

Next, a case where the calibration is discontinued in the middle of thesecond sequence will be described with reference to a flowchartillustrating the second sequence in FIG. 7 .

In step S1001, the CPU 401 causes the printer B to form a pattern image,causes the sensor 160 to detect the pattern image on the transfer belt111, and calculates image forming conditions based on the detectionresult of the sensor 160. In step S1002, the CPU 401 changes the imageforming conditions to VDn and LPWn. The CPU 401 stores the image formingconditions (VDn and LPWn) calculated in step S1001 and the image formingconditions (VDo and LPWo) used before the pattern image is formed inrespectively different areas of the memory 402.

In the second sequence, the test charts for different screens are outputone by one. First, in step S1003, the test chart 801 a for the screenwith low screen rulings is output. Before the test chart 801 a isprinted, the CPU 401 displays the UI (FIG. 8 ) for the user to instructdiscontinuation of the calibration on the display of the operation panelU. In step S1004, the CPU 401 determines whether discontinuation of thecalibration has been instructed before the test chart 801 a is read. Inresponse to selection of discontinuation of the calibration by the uservia the UI of FIG. 8 , the operation panel U transmits thediscontinuation instruction to the CPU 401.

In a case where the CPU 401 does not receive the discontinuationinstruction in step S1004 and start of reading is instructed (NO in stepS1004), the processing proceeds to step S1005. In step S1005, the CPU401 reads the test chart 801 a in the platen reading. In step S1006, theCPU 401 generates the gradation correction condition (LUTa1)corresponding to the screen with low screen rulings, and updates thegradation correction condition (LUTa1) stored in the memory 402. Next,in step S1007, the CPU 401 determines whether reading of all of the testcharts for the screens printed in the calibration has been completed.

In a case where reading of all of the test charts for the screens hasnot been completed in step S1007 (NO in step S1007), the processingreturns to step S1003, and the CPU 401 causes the printer B to outputthe test chart 801 b for the other screen (screen with high screenrulings). The CPU 401 similarly reads the test chart 801 b in the platenreading, generates the gradation correction condition (LUTa2), andupdates the gradation correction condition (LUTa2) stored in the memory402.

After reading of the test charts for all of the screens is completed instep S1007 (YES in step S1007), the CPU 401 ends the calibrationprocessing.

In contrast, in a case where the CPU 401 receives the discontinuationinstruction in step S1004 (YES in step S1004), then in step S1008, theCPU 401 reads out the image forming conditions used before the patternimage is formed, from the memory 402, and resets the image formingconditions to the original values (VDo and LPWo). Thereafter, the CPU401 ends the calibration processing.

How the discontinuation is instructed is not limited to theconfiguration in which the discontinuation instruction is transmitted inresponse to operation of the operation panel U by the user. For example,in the case where a jam occurs in the printer B while the printer Boutputs the test chart 801 a (or test chart 801 b), the CPU 401 receivesthe discontinuation instruction. Further, for example, in the case wherethe main power supply of the image forming apparatus 1000 is turned offduring the period from when the image forming conditions are determinedbased on the detection result of the sensor 160 until the gradationcorrection condition (LUTa) is generated based on the reading result ofthe test image, the CPU 401 receives the discontinuation instruction. Ina case where the CPU 401 receives the discontinuation instruction duringthe second sequence, the CPU 401 resets the image forming conditions tothe original values (VDo and LPWo), and ends the calibration processing.

Even in the case where the calibration is discontinued, the imageforming apparatus 1000 sets the image forming conditions to the imageforming conditions before the pattern image is formed. The image formingapparatus 1000 thus can perform image formation with an appropriatecombination of image forming conditions and the gradation correctioncondition.

According to the exemplary embodiment of the disclosure, even in thecase where the calibration is discontinued, it is possible to preventthe density of the output image from being erroneously adjusted.

Next, in a second exemplary embodiment, another case where thecalibration is discontinued in the middle of the second sequence will bedescribed with reference to a flowchart illustrating the second sequencein FIG. 9 . In a case where the discontinuation instruction is receivedduring a period from when the gradation correction condition (LUTa1) isgenerated until the gradation correction condition (LUTa2) is generated,the CPU 401 determines image forming conditions before the pattern imageis formed, as the image forming conditions for the screen with highscreen rulings.

In an example illustrated in FIG. 9 , the test chart 801 a and the testchart 801 b are sequentially output. A test image for the screen withlow screen rulings is formed in a first sheet, and a test image for thescreen with high screen rulings is formed in a second sheet. Processingin steps S1201 to S1207 in FIG. 9 is similar to the processing in stepsS1001 to S1007 in FIG. 7 . Therefore, description of the processing insteps S1201 to S1207 will be omitted.

After reading of the test charts for all of the screens is completed instep S1207 (YES in step S1207), then in step S1208, the CPU 401 discardsthe image forming conditions (VDo and LPWo) before the pattern imagestored in the memory 402 is formed. The CPU 401 then ends thecalibration processing.

In a case where reading of the test charts for all of the screen is notcompleted in step S1207 (NO in step S1207), the processing returns tostep S1203, and the CPU 401 causes the printer B to output the testchart 801 b for the other screen (screen with high screen rulings). Whenthe discontinuation instruction is not output, the CPU 401 similarlyreads the test chart 801 b in the platen reading, generates thegradation correction condition (LUTa2), and updates the gradationcorrection condition (LUTa2) stored in the memory 402.

In contrast, in a case where the discontinuation instruction is receivedin step S1204 (YES in step S1204), the processing proceeds to stepS1209. A case where the CPU 401 receives the discontinuation instructionafter the LUTa1 is generated and before the test chart 801 b is readwill be described below. In step S1209, the CPU 401 stores both of theimage forming conditions (VDn and LPWn) calculated in step S1201 and theimage forming conditions (VDo and LPWo) before the pattern image isformed, in the memory 402 without discarding the image formingconditions (VDo and LPWo). Thereafter, in step S1210, the CPU 401 storesthe canceled screen. In this example, the CPU 401 stores the screen withthe high screen rulings as the canceled screen. The CPU 401 then endsthe calibration processing.

In a case where the image forming apparatus 1000 forms an image by usingthe screen with low screen rulings after the calibration is ended, theCPU 401 forms the image by using the image forming conditions (VDn andLPWn) and the gradation correction condition (LUTa1). In a case wherethe image forming apparatus 1000 forms the image by using the screenwith high screen rulings after the calibration is ended, the CPU 401forms the image by using the image forming conditions (VDo and LPWo) andthe gradation correction condition (LUTa2). The gradation correctioncondition (LUTa2) corresponding to the screen with high screen rulingsis not updated by the calibration.

FIGS. 10A to 10C are tables illustrating combinations of the imageforming conditions (VD and LPW) and the gradation correction condition(LUT) determined by the CPU 401 through the calibration. In the casewhere the discontinuation is not instructed during the calibration, newimage forming conditions (VDn and LPWn) and an updated gradationcorrection condition (LUTa) are applied to all of the screens asillustrated in FIG. 10A.

In the case where the test chart 801 a is read but the test chart 801 bis not read, image forming conditions and a gradation correctioncondition are used depending on the screen as illustrated in FIG. 10B.In the case where the image is formed by using the screen with lowscreen rulings, new image forming conditions (VDn and LPWn) and a newgradation correction condition (LUTa1) are used. In contrast, in thecase where the image is formed by using the screen with high screenrulings, old image forming conditions (VDo and LPWo) and an oldgradation correction condition (LUTa2) are used.

In a case where, in the calibration in which three test charts areprinted, the second test chart is read but the third test chart is notread, old image forming conditions are used when the image is formed byusing the third screen as illustrated in FIG. 10C.

As described above, even in the case where the CPU 401 receives thediscontinuous instruction of the calibration, the image formingapparatus 1000 can form an image based on an appropriate combination ofimage forming conditions and a gradation correction condition. Thus,even in the case where calibration is discontinued, the image formingapparatus 1000 can prevent the density of an output image from beingerroneously adjusted.

According to the exemplary embodiments of the disclosure, even in a casewhere calibration is discontinued, it is possible to prevent the densityof an output image from being erroneously adjusted.

While the disclosure has been described with reference to exemplaryembodiments, it is to be understood that the disclosure is not limitedto the disclosed exemplary embodiments. The scope of the followingclaims is to be accorded the broadest interpretation so as to encompassall such modifications and equivalent structures and functions.

What is claimed is:
 1. An image forming apparatus comprising: an imageprocessor configured to convert image data based on a conversioncondition; an image former configured to form an image based on an imageforming condition and the image data converted by the image processor; atransfer member onto which a pattern image is formed; a detectorconfigured to detect the pattern image on the transfer member; a readingsensor configured to read a test image formed on a sheet; a controllerconfigured to: control the image former to form the pattern image on thetransfer member; update a first image forming condition to a secondimage forming condition based on a detection result of the pattern imagedetected by the detector, wherein the first image forming condition isused for an image formation by the image former before the pattern imageis formed; control the image former to form the test image differentfrom the pattern image on the sheet based on the second image formingcondition; generate the conversion condition based on a reading resultof the test image read by the reading sensor; and return the secondimage forming condition to the first image forming condition, in a casewhere a user cancel instruction to cancel generation of the conversioncondition is received before reading the test image by the readingsensor.
 2. The image forming apparatus according to claim 1 furthercomprising a platen on which a sheet is to be placed, and wherein thereading sensor reads the test image on the sheet placed on the platen.3. The image forming apparatus according to claim 1 further comprising adocument feeder including a stacking tray on which a sheet is to bestacked; a conveying roller configured to convey the sheet stacked onthe stacking tray; a discharging roller configured to discharge thesheet; and a discharge tray on which the sheet is discharged by thedischarging roller, wherein the reading sensor reads the test image onthe sheet conveyed by the conveying roller.
 4. The image formingapparatus according to claim 1, wherein the conversion condition is atone correction condition.
 5. The image forming apparatus according toclaim 1, wherein the image former comprises a photosensitive member, acharger that charges the photosensitive member, a light source thatexposes the photosensitive member charged by the charger to form anelectrostatic latent image with light, and a developing sleeve thatdevelops the electrostatic latent image formed on the photosensitivemember, and wherein the image forming condition is for a chargingvoltage to be applied to the charger that charges the photosensitivemember.
 6. The image forming apparatus according to claim 1, wherein theimage former comprises a photosensitive member, a charger that chargesthe photosensitive member, a light source that exposes thephotosensitive member charged by the charger to form an electrostaticlatent image with light, and a developing sleeve that develops theelectrostatic latent image formed on the photosensitive member, andwherein the image forming condition is for laser power of the lightsource that exposes the photosensitive member.
 7. The image formingapparatus according to claim 1, wherein the image former comprises aphotosensitive member, a charger that charges the photosensitive member,a light source that exposes the photosensitive member charged by thecharger to form an electrostatic latent image with light, and adeveloping sleeve that develops the electrostatic latent image formed onthe photosensitive member, and wherein the image forming condition isfor a developing voltage to be applied to the developing sleeve thatdevelops the electrostatic latent image.